The etiology of human breast cancer is thought to involve a complex interplay of genetic, hormonal, and dietary factors that are superimposed on the physiological status of the host, Attempts to derive a cohesive picture of how these factors participate in the etiology of breast cancer have been confounded by a lack of information on specific mutations associated with the Initiation and progression of the disease. We have undertaken an ongoing program aimed at determining, on a molecular level, those genetic alterations in primary breast tumor DNA that have a statistically significant association with the patients history, characteristics of the tumor, and the patients prognosis. The most frequent type of mutation is loss of heterozygosity (LOH) at specific regions of the cellular genome in tumor DNA. In previous studies, we have found LOH on chromosomes 1p, 1q, 3p, 11p, 13q, 17p, 17q, and 18q.Our current results demonstrate LOH of the c-met proto-oncogene on chromosome 7q in 40.5% of the tumor DNAs. This genetic alteration was not associated with the lymph mode status of the patient nor other standard prognostic features of the tumor. However, patients having tumors with LOH on chromosome 7q had a significantly shorter disease-free interval (p=0.00022) and overall survival (P=0.0036). A separate panel of 96 primary breast tumors was evaluated for their proliferative index by their ability to incorporate BruD in culture. A significant association (p=0.022) was found between those tumors having an elevated BruD labeling index and LOH at the pYNZ22.1 locus on chromosome 17p. In contrast, no association was found between the tumor BrdU labeling index and LOH at the more telemetric locus pl44D6 on chromosome 17p nor LOH on chromosomes 1p, 3p, 13q, or 18q. To determine whether the p53 tumor suppressor gene Is a target for LOH on chromosome 17 we examined 26 tumors by RNAse protection assays and nucleotide sequence analysis for p53 mutations. The same three tumors were found to have point mutations in the p53 gene. We also did single strand conformation polymorphism (SSCP) analysis which proved more sensitive in the detection of mutations. Taken together, the results showed that a total of 12 p53 mutations in 11 tumors (46%). Currently we are determining whether p53 mutations are linked to the proliferative index of the tumor.